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Keywords:

  • Antarctica;
  • Greenland;
  • gravity;
  • oblateness

[1] The Earth's rotation causes mass from the ductile mantle to bulge at the equator, making the radius of the Earth about 21 kilometers greater at the equator than at the poles. Over the past 20,000 or so years, the Earth has been becoming more round as it adjusts to the withdrawal of vast continental glaciers after the last ice age: Without the weight of ice pressing down, land has rebounded to give the Earth a more spherical shape. This in turn means that the Earth|'s geoid—the average gravity field across the globe—also became more round. However, in the early 1990s, scientists began to notice that postglacial rebound was starting to become offset by something else, causing the Earth's gravity field to cease changing shape.